PROJECT SUMMARY Parkinson?s disease (PD) is associated with abnormally increased, synchronized and oscillatory neuronal activity in the basal ganglia output circuitry, i.e., the subthalamic nucleus (STN) and the major target of its efferents, the internal pallidal segment (GPi). These changes are thought to be causally related to the emergence of parkin- sonism. Modulation of STN output with neurosurgical methods such as deep brain stimulation (DBS) have be- come standard treatments for advanced PD. However, these interventions are non-specific and can have signif- icant side effects. This project explores novel regulatable genetic approaches to reduce the parkinsonism-asso- ciated activity changes in STN and GPi and to ameliorate parkinsonism with fewer side effects (and potentially greater effects) than achieved with the currently available surgical methods. Under aim 1, we will examine the electrophysiologic and behavioral effects of doxycycline-controlled tetanus toxin light chain (TeTxLC) based si- lencing of synaptic transmission at efferents of STN neurons in parkinsonian (MPTP-treated) monkeys. The use of this approach is based on the well-documented effectiveness of STN or GPi inactivation in parkinsonian mon- keys, and on preliminary studies in rodents. The experiments under aim 2 will explore in rodents whether par- kinsonism can be treated by altering plasticity at synapses within the STN. The role of maladaptive plasticity in the STN of parkinsonian animals has recently been stressed in both non-human primates and rodent species, and there is preliminary evidence that it also applies to human patients with PD. We will explore two new regu- latable genetic approaches aimed at reducing these changes in the STN of 6-hydroxy dopamine (6-OHDA) treated, parkinsonian rats. In one approach, transmission at a sub-type of glutamatergic NMDA receptors (GluN2D receptors) which is strongly enriched in the STN will be manipulated by using a membrane-tethered GluN2D-specific toxin, and, as an alternative approach, microRNA-mediated Grin2D knockdown. Secondly, based on preliminary data in other fields, we will examine the effects of blocking gliotransmission using TeTxLC targeted to astrocytes in the STN to reduce (maladaptive) synaptic plasticity. The planned collaborative work is highly innovative, using new chemogenetic tools to achieve antiparkinsonian effects in parkinsonian primates and rodents. The results of our studies may provide guidance for larger systematic projects to explore these novel approaches. If successful, the new methods could be rapidly translated to improve the care of PD patients.